In wireless communication systems that employ beamforming of transmissions from a plurality of antennas of a first device to a second device (having one or more antennas), it is important to have reliable information about the channel conditions between the antennas of the first and second devices. One type of beamforming technique, known as implicit beamforming, uses uplink traffic received by the first device from the second device to capture the most up-to-date channel information. That channel information is converted into a beamforming vector used for sending a beamformed transmission from the first device to the second device.
In some wireless communication systems, such as those that operate in accordance with the IEEE 802.11n and 802.11ac standards, single channels can be combined to allow for wider bandwidth transmissions. Thus, one channel is designated a primary channel and the adjacent channel is designated a secondary channel, and the secondary channel can be aggregated together with the primary channel for a wider bandwidth transmission. For example, according to one feature of the 802.11n standard, a “legacy duplicate mode” packet is sent over 40 MHz whereby the same data (acknowledgment packets) are transmitted over two adjacent 20 MHz channels.
When receiving legacy duplicate mode packets, currently designed and deployed radio transceiver chipsets for IEEE 802.11n discard the secondary channel's packet and only demodulate the primary signal. As a consequence, the transceiver chipset does not output channel state information (CSI) for the secondary channel because the transceiver chipset cannot determine if it is a duplicate mode packet or just a 20 MHz legacy packet in the secondary channel. It would be beneficial to know if the packet in the secondary channel is from an intended client or some adjacent/overlapping AP/client in order to know whether to use the CSI for the secondary channel in computing downlink transmit beamforming weights to transmit to a particular client. If the AP is not able to know when to discard the CSI for the secondary channel, it is possible that the AP may overwrite good/reliable beamforming weight information with unreliable information.